1. Technical Field
The invention relates to forming container bodies from a blank of metal, and, in particular, to forming such bodies in a double-acting press which reduces the forces exerted on the press by sequentially performing the various operations on the blank of metal when forming the container body.
2. Background Information
It is well known in the container-forming art to form two-piece containers, that is, containers in which the walls and bottom of the container are a one-piece member, and the top or end closure is a separate piece, by means of stamping blanks from a strip of metal sheet, and then subsequently drawing the desired configuration into the drawn blank.
In broad terms, the prior art discloses, starting with flat material either in sheet or coil form, blanking material from the sheet stock, and then drawing it into a cup for further redrawing into a final container in the same press or in subsequent operations. There are a considerable number of prior art patents illustrating various approaches to this formation using either single or double-acting presses. Generally, these prior art presses will simultaneously form a plurality of the container bodies in a single stroke of the single or double-acting press. For example, eight, ten, twelve or more container bodies are formed simultaneously by the single stroke of the press, whether it be a single-action or double-action press.
However, one problem that is encountered with these presses is that they produce excessive noise and forces on the press due to the simultaneous engagement of the initial blank sheet with the plurality of cutting dies or cut edges, followed by the simultaneous pressure holding engagement of the peripheral edges of the blanks, followed by the simultaneous drawing of all of the cups or container bodies by the movement of a plurality of inner punch members by the inner ram of a double-acting press. These forces present maintenance problems on the dies and press, as well as limiting the number of container bodies or end shells which can be produced in a single stroke, or require a larger press having higher tonnages.
It is always desirable to produce an apparatus or forming dies and associated method which is capable of producing a plurality of container bodies from steel or aluminum or other stock materials, with a low tonnage press as possible, and with reduced noise and vibrations, while providing the maximum output from the press. However, as indicated above, the forces exerted on the press and dies during the initial blanking, pressure holding and subsequent drawing, limit the output of the press.
Therefore, the need exists for an improved method and apparatus for providing maximum output from a press with as low tonnage rating as possible, while reducing noise and working forces on the apparatus and press.